1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to managing digital content, and more particularly, to managing digital content to prevent the digital content from being further leaked when an encryption key of the digital content is leaked.
2. Description of the Related Art
Recently, transmission of digital content using various communication media such as the Internet, ground waves, cables, and satellites has rapidly increased, and the sale and lending of the digital content using mass recording media such as compact discs and digital versatile discs (DVDs) has also rapidly increased. Accordingly, digital rights management, which is a means for protecting copyright of digital content has been spotlighted. In particular, research into allowing a legal user of a home domain to freely receive various content services using devices belonging to the home domain is actively ongoing. These devices such as digital televisions or personal digital assistants (PDAs) belonging to the same domain share their content with the other devices.
However, in order to ideally protect the content, only devices which are registered in the domain, can use the content in the domain, and devices which are not registered in the domain cannot use the content in the domain. Accordingly, the devices which are registered in the domain share a domain key. Hereinafter, this domain key will be described in detail.
FIG. 1 is a view for illustrating a method of managing digital content in a general domain. As illustrated in FIG. 1, a domain X includes a device A, a device B, and a device C as domain members. A domain managing apparatus manages these devices A, B, and C. When digital content C is input to the domain X, the domain managing apparatus encrypts the digital content C using a specific encryption key K and transmits encrypted digital content E(K, C) to the devices A, B, and C according to the requests of the devices A, B, and C.
Meanwhile, the devices A, B, and C previously receive a domain key from the domain managing apparatus. The encryption key K used for encrypting the digital content C can be decrypted only by the domain key. In a symmetric key, the domain key is identical to the encryption key. Thus, the digital content C can be shared among the members of the domain X. In other words, although a device which is not registered in the domain X, can receive the encrypted digital content E(K, C), the device cannot decrypt the received E(K, C) because the device does not have the domain key.
However, when the domain key is leaked and the domain managing apparatus does not detect the leakage of the domain key, the digital content input to the domain may be leaked. In other words, when the domain key is leaked or cracked to decrypt the encrypted digital content E(K, C) and the domain managing apparatus does not detect the leakage of the domain key, the digital content, which will be input to the domain X later, may be encrypted using the domain key, and the encrypted digital content E(K, C) may be then decrypted. Thus, the digital content, which must be shared in only the domain, cannot be protected. In addition, this problem may be caused even when digital content used only in a specific device is encrypted using a unique encryption key of the device.